/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.zookeeper.server.quorum;

import java.io.IOException;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.jute.Record;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.zookeeper.server.FinalRequestProcessor;
import org.apache.zookeeper.server.Request;
import org.apache.zookeeper.server.RequestProcessor;
import org.apache.zookeeper.server.SyncRequestProcessor;
import org.apache.zookeeper.server.ZKDatabase;
import org.apache.zookeeper.server.persistence.FileTxnSnapLog;
import org.apache.zookeeper.txn.TxnHeader;

/**
 * Just like the standard ZooKeeperServer. We just replace the request
 * processors: FollowerRequestProcessor -> CommitProcessor ->
 * FinalRequestProcessor
 * 
 * A SyncRequestProcessor is also spawned off to log proposals from the leader.
 */
public class FollowerZooKeeperServer extends LearnerZooKeeperServer {
	private static final Logger LOG = LoggerFactory.getLogger(FollowerZooKeeperServer.class);

	CommitProcessor commitProcessor;

	/*
	 * Pending sync requests
	 */
	ConcurrentLinkedQueue<Request> pendingSyncs;

	LinkedBlockingQueue<Request> pendingTxns = new LinkedBlockingQueue<Request>();

	SyncRequestProcessor syncProcessor;

	/**
	 * @param port
	 * @param dataDir
	 * @throws IOException
	 */
	FollowerZooKeeperServer(FileTxnSnapLog logFactory, QuorumPeer self, DataTreeBuilder treeBuilder, ZKDatabase zkDb)
			throws IOException {
		super(logFactory, self.tickTime, self.minSessionTimeout, self.maxSessionTimeout, treeBuilder, zkDb, self);
		this.pendingSyncs = new ConcurrentLinkedQueue<Request>();
	}

	/**
	 * When a COMMIT message is received, eventually this method is called, which
	 * matches up the zxid from the COMMIT with (hopefully) the head of the
	 * pendingTxns queue and hands it to the commitProcessor to commit.
	 * 
	 * @param zxid - must correspond to the head of pendingTxns if it exists
	 */
	public void commit(long zxid) {
		if (pendingTxns.size() == 0) {
			LOG.warn("Committing " + Long.toHexString(zxid) + " without seeing txn");
			return;
		}
		long firstElementZxid = pendingTxns.element().zxid;
		if (firstElementZxid != zxid) {
			LOG.error("Committing zxid 0x" + Long.toHexString(zxid) + " but next pending txn 0x"
					+ Long.toHexString(firstElementZxid));
			System.exit(12);
		}
		Request request = pendingTxns.remove();
		commitProcessor.commit(request);
	}

	public Follower getFollower() {
		return self.follower;
	}

	@Override
	public int getGlobalOutstandingLimit() {
		return super.getGlobalOutstandingLimit() / (self.getQuorumSize() - 1);
	}

	@Override
	public Learner getLearner() {
		return getFollower();
	}

	@Override
	public String getState() {
		return "follower";
	}

	public void logRequest(TxnHeader hdr, Record txn) {
		Request request = new Request(null, hdr.getClientId(), hdr.getCxid(), hdr.getType(), null, null);
		request.hdr = hdr;
		request.txn = txn;
		request.zxid = hdr.getZxid();
		if ((request.zxid & 0xffffffffL) != 0) {
			pendingTxns.add(request);
		}
		syncProcessor.processRequest(request);
	}

	@Override
	protected void setupRequestProcessors() {
		RequestProcessor finalProcessor = new FinalRequestProcessor(this);
		commitProcessor = new CommitProcessor(finalProcessor, Long.toString(getServerId()), true);
		commitProcessor.start();
		firstProcessor = new FollowerRequestProcessor(this, commitProcessor);
		((FollowerRequestProcessor) firstProcessor).start();
		syncProcessor = new SyncRequestProcessor(this, new SendAckRequestProcessor((Learner) getFollower()));
		syncProcessor.start();
	}

	@Override
	public void shutdown() {
		LOG.info("Shutting down");
		try {
			super.shutdown();
		} catch (Exception e) {
			LOG.warn("Ignoring unexpected exception during shutdown", e);
		}
		try {
			if (syncProcessor != null) {
				syncProcessor.shutdown();
			}
		} catch (Exception e) {
			LOG.warn("Ignoring unexpected exception in syncprocessor shutdown", e);
		}
	}

	synchronized public void sync() {
		if (pendingSyncs.size() == 0) {
			LOG.warn("Not expecting a sync.");
			return;
		}

		Request r = pendingSyncs.remove();
		commitProcessor.commit(r);
	}
}
